1. Field of the Invention
The present invention relates to a forming method for forming an assembly of a bead core and an apex rubber, and more particularly to a method of forming an apex rubber having a triangular cross sectional shape on an outer peripheral surface in a radial direction of a bead core, by winding a ribbon-shaped rubber strip.
2. Description of the Related Art
In a pneumatic tire, demand characteristics are different in respective positions. Accordingly, the pneumatic tire is formed by various tire rubber members having differentiated compositions and cross sectional shapes, for example, a tread rubber, a sidewall rubber, a clinch rubber, an inner liner rubber and the like. conventionally, in each of the tire rubber members, there is used a molded body extrusion molded by a rubber extruding machine so as to have a desired cross sectional shape. Further, each of the rubber members is formed by winding the molded body on a molding drum or the like at one circle, in a green tire molding step.
With respect to the extrusion molding method, a change to a strip wind method has been promoted in recent years. This strip wind method is a method of directly forming a strip wind body having a desired cross sectional shape as a tire rubber member on a cylindrical molding drum by spirally winding a ribbon-shaped rubber strip. In this method, great advantages are applied to the tire having a strong tendency of a large item small scale production, for example, it is not necessary to store the molded body for the rubber member as an intermediate stock, it is not necessary to use a large-scaled rubber extruding machine, and the like.
However, the apex rubber corresponding to one of the tire rubber member has a special cross sectional shape extending in a triangular cross sectional shape toward an outer side in a radial direction from an outer peripheral surface of the bead core. Accordingly, it is technically hard to form easily and with a high quality in accordance with the strip wind method. Further, the apex rubber is treated as an assembly previously bonded to the bead core integrally, in a green tire manufacturing line. For these reasons, the formation of the apex rubber in accordance with the strip wind method has not yet been made practicable.